The invention relates to a wireless network with a plurality of network nodes, each of which consists of at least one electrical apparatus and at least one radio device which are arranged to exchange data via a wireless medium.
A wireless network of this kind is known from the document xe2x80x9cTechnologie drahtloser Netzexe2x80x9d by Elmar Txc3x6rxc3x6k, Funkschau No. 22, 1998, pp. 20 to 25; this document describes the construction of a wireless network with a plurality of network nodes. A plurality of electrical apparatus, for example, monitors, computers etc. and a radio device are interconnected, via a bus system, in a network node. Data is exchanged with other radio devices via the radio device of each network node. The cited document does not refer to clock synchronization of all network nodes.
It is an object of the invention to provide a wireless network in which the clocks of the individual network nodes are synchronized with one another.
This object is achieved by a wireless network of the kind set forth which is characterized in accordance with the invention in that a network node includes a clock supply for supplying all electrical apparatus and the radio device with its clock, that a network node which is designated as the main network node is arranged to transmit, via its radio device, a synchronization pattern which is dependent on the clock of its clock supply, that all other network nodes, designated as secondary network nodes, are assigned to different, hierarchically ordered distance classes in dependence on their distance from the main network node which is assigned to the highest distance class, that all secondary network nodes of a distance class are arranged to transmit, via their respective radio device, a synchronization pattern which is dependent on the clock of their respective clock supply and characterizes the distance class, and that a secondary network node is arranged to synchronize its clock supply by means of at least one received synchronization pattern of a hierarchically higher distance class.
In accordance with the invention, a main network node transmits a synchronization pattern via the wireless medium, which synchronization pattern is,forwarded by secondary network nodes in the various distance classes so that a secondary network node of the hierarchically lowest distance class is indirectly synchronized by the clock of the clock supply of the main network node. In this context wireless transmission is to be understood to mean a radio, infrared, ultrasound etc. transmission.
Claim 2 discloses how a secondary network node finds its distance class after activation. In the case of a moving secondary network node and/or main network node, the distance class of a secondary network node is liable to change. The claims 3 and 4 describe the steps taken by a mobile secondary network node in order to determine its optimum distance class in all circumstances.
A secondary network node includes a correlator which is arranged to determine whether a given synchronization pattern has been received with adequate reception quality. As is disclosed in claim 5, during the time in which a synchronization pattern is awaited a secondary network node is arranged to correlate the received signal with a stored synchronization pattern and to indicate the reception of the synchronization pattern if the correlation result corresponds to an expected value. The claims 6 and 7 describe the determination of the synchronization instant for the clock synchronization in a secondary network node.
Claim 8 discloses the construction of a radio device. A protocol device in the radio device executes various protocols for the transmission of data for the wireless medium and determines, for example by comparing the pulse-shaped signal supplied by a correlator with a threshold value, whether the reception quality of a synchronization pattern is adequate. The correlator may be included, for example in a modem of the radio device.
The synchronization patterns of each distance class are different. In order to simplify the construction of the correlator, each synchronization pattern may include an identical part and a second, different part in order to characterize a respective distance class. The correlator then correlates the first part of the synchronization pattern with a stored first part of the synchronization pattern and, after detection of an adequate reception quality, the protocol device then evaluates, for example, the characterization contained in the second part of the synchronization pattern.
The invention also relates to a network node of a wireless network which includes a plurality of further network nodes, which network node consists of at least one electrical apparatus and at least one radio device which are arranged to exchange data via a wireless medium. The network node includes a clock supply for supplying all electrical apparatus and the radio device with its clock. The network node which is designated as a secondary network node belongs to a distance class which forms part of a plurality of hierarchically ordered distance classes; its distance class is dependent on its distance from a main network node which is assigned to the highest distance class. The secondary network node is arranged to transmit, via its radio device, a synchronization pattern which is dependent on the clock of the relevant clock supply and characterizes its distance class, and to synchronize its clock supply by means of at least one received synchronization pattern of a hierarchically higher distance class.